Inkjet recording is a recording system for forming characters or images, comprising directly jetting ink droplets from very fine nozzles to a recording medium, and depositing the ink droplets on the recording medium. This system has advantages that not only the used device shows excellent operability at a low level of noise, but also the coloration is facilitated and plain paper can be used as a recording medium. Therefore, this system has been widely used in the recent years.
As an ink set comprising a black ink and a color ink usable for color inkjet printers, there have been known an ink set comprising an acidic black ink comprising an acidic carbon black, a basic surfactant and a water-soluble organic solvent, and a basic color ink (Japanese Patent Laid-Open No. Hei 9-183224); an ink set comprising a black ink comprising a self-dispersible carbon black in which at least one hydrophilic group is bonded directly or via the other group of atoms to the surface of the carbon black, and a color ink comprising a colorant having a polarity opposite to the colorant used in the black ink (Japanese Patent Laid-Open No. Hei 10-140064); and the like.
However, the printouts formed by using these inks are wrong especially in fixing abilities such as rubbing resistance and high-lighter fastness in the black ink, and are not sufficiently satisfactory in these properties, while printouts formed by using there ink sets are excellent in bleeding resistance.